Current from transformer neutrals on ground

[Overunity_1]

At any of our substations, we can measure current on the structure ground wires. This is to be expected as the transformer is unbalanced, so we are seeing current from the neutral. My question is, how does this current flow? What is the path? It would seem to me that the structure would not complete a circuit as it is open essentially, and the ground cable is it's only connection.

 

[Kiribanda]

1)It looks like these are unbalanced currents due to single phase loading.They must flow in the neutral.
It seems a proper neutral conductor is not provided.

2)They may be GF currents too. But I believe that then your GF protection should have worked.

3)Can you please upload the SLD? By looking at the SLD more responses will come.

 

[Palletjack]

You put an ammeter on the grounding wires on the structure and see amps, correct? How high are these amps?
Some is to be expected.
Imbalance currents come back to source through the neutral. If something happens to your neutral, say a bad or broken connection, currents will flow back to the source proportional to resistance through the earth.
If there are any dairy farms close your farmers will definitely let you know about it.

 

[Parchie]

@Overunity_1,
What @ Kiribanda said, these currents should be running at the neutral wires! I there are no ground, the ground conductors shall have no currents, IMO.

 

[davidbeach]

There will almost always be induced charge, and therefore current, on ground conductors out in the open above ground.

 

[cuky2000]

The current return to the source via the neutral and the conductive earth path.

 

[bacon4life]

Structures with a single metal ground wire also have 2 kinds of nonmetallic circuits:
1) Capacitive coupling. The amount of current on the ground wire is correlated to the magnitude of the voltage, the asymmetry of the tower arrangement, and inversely correlated to the spacing between the structure and the phase wires. An example of this is the barb wire on top of the substation fence will more ground current flowing when the phase conductors passing over it are arranged vertically as opposed horizontally. Anther example of capacitive coupling is the arcing as a helicopter attaches to a high voltage line.

2) Inductive(magnetic) coupling. The amount of current on the ground wire is correlated with the current flow on the phase wires and the length of structure that runs parallel to the phase wires. This type of coupling is why utilities often prohibit metallic fences along transmission rights of way.

 

[prc]

In power transformers, there can be two types of spurious currents - one through the neutral bushing of a star connected winding to ground, second through the grounding wire from tank to ground.

The neutral current can be from a load having harmonic currents(in case of distribution transformers feeding electronic loads) , unbalanced loads, improperly transposed transmission lines, tap changer alignment issues( OLTC in each phase with improper alignments) or voltage difference with grounding grid potential (large power stations)

Grounding current can be due to potential difference to grounding grid and tank subjected to very high leakage flux from windings. Maximum that came to my notice was in a rectifier transformer in an aluminum smelter. The grounding current was 800A which got reduced to 600 A when one of the tank grounding point was removed from ground connection.

 

[mc5w]

MSHA requires induced voltage in the equipment ground due to air core transformer action and normal current flow to be limited to 10 volts or less. Presumable US Bureau of Shipping has a similar or identical for commercial shipyards particularly shore to ship power. This is generally a problem with the longer circuits characteristic of mines, shipyards, and utility power transmission and distribution. I have seen what used to a be 34.5 KV 3 phase line ( downgraded by Cleveland Electric Illuminating Company to 7,620Y13,200 volts ) that had transpositions once every half mile or so, I have also seen a 69 KV line in northern Kentucky along I-71 with frequent transpositions.